Effect pigments, also known as pearlescent pigments or nacreous pigments, are used to impart a pearlescent luster, metallic luster and/or multi-color effect approaching iridescent, to a material. For instance, black effect pigments based on flake-form substrates are of particular interest in cosmetics. One of the primary black effect pigments approved for cosmetic applications includes Fe3O4-based effect pigments.
U.S. Pat. Nos. 3,926,659, 7,303,622 and U.S. publication no. 2007/0032573 disclose Fe3O4 based effect pigments.
Fe3O4-based effect pigments tend to be very stable and not subject to decomposition the way many color based pigments, such as carmine are. However, Fe3O4-based effect pigments normally do not provide sufficient blackness.
In addition, Fe3O4 does not bind well to platy substrates. For example, Fe3O4 adhesion to substrates such as mica and perlite is weak. Accordingly, once the Fe3O4 coated substrates are subjected to mechanical shear, such as hand mixing of the product in a lacquer, the Fe3O4 layer or coating is easily removed from the surface of the substrate. This removal of Fe3O4 coating or layer from the substrate can cause “staining” issues.
Thus, there is an on-going need in the art for black effect pigment compositions with improved darkness and improved adhesion to platy substrates.